1. Field of the Invention
The present invention relates to a lens apparatus and more particularly to a lens apparatus having a zoom, lens.
2. Description of the Related Art
In recent times, zoom lens apparatuses for still image shooting or video shooting that are small in size and light in weight in favor of portability are demanded. For this reason, many rear focus type zoom lens apparatuses in which a focus lens for focus adjustment is located closer to the image pickup element than a zoom lens for varying the magnification have been developed.
In the rear focus type zoom lens apparatus, in order to perform zooming while maintaining the imaging position, it is necessary to control the position of the focus lens appropriately with changes of the position of the zoom lens. The controlled position of the focus lens with a change in the position of the zoom lens cannot be computed by simple calculation. For this reason, control positions of the focus lens with variations in the position of the zoom lens at every in-focus distance are typically stored in advance as table data in a ROM, and the controlled position of the focus lens is determined using the table data.
With increases in the image quality of image pickup apparatuses, rear focus type zoom, lens apparatuses tend to have small depths of field. In consequence, high accuracy in the aforementioned controlled position of the focus lens is required. To meet this requirement, finer (or more detailed) table data is needed, necessitating a ROM having a large capacity.
As a solution to the above-described problem, Japanese Patent Application Laid-Open No. H06-62302 teaches to employ table data and interpolation calculation in combination to thereby determine a controlled position of the focus lens at high accuracy while preventing an increase in the ROM capacity.
However, the prior art technique disclosed in Japanese Patent Application Laid-Open No. H06-62302 employs three steps of interpolation processing that take processing time, leading to long time taken from the detection of the zoom position to the start of driving of the focus lens. Consequently, quick zooming operation will lead to a large difference between the focus lens position that, brings an object in focus at the time of detection of the zoom position and the focus lens position that brings the object in focus at the time of driving of the focus lens, likely leading to a focus error.